Apparatus for testing hardness



July 9, 1940. Q ZAMBQNL 2,207,502

APPARATUS FOR TESTING HARDNESS Filed March 11, 1937 2 Sheets-Sheet l"TEJQ- i C5ar6 Zam 60 INVENTOR ATTORNEY July 9, 1 c. ZAMBONI APPARATUSFOR TESTING HARDNESS 2 Sheets-Sheet 2 Filed March 11, 1937 (365G reZea/wh INVENTOR ATTORNEY Patented July 9, 1940 UNITED STATES APPARATUSFQ-R TESTING HARDNESS Cesare Zamboni, Rome, Italy Application March 11,937, Serial No. 130,324 In Italy March 13, 1936 2 Claims.

The present invention relates to apparatus for testing the hardness ofmaterials, and particularly of hardened cement pastes and conglomerates,by measuring. the rebound ofa pivotally suspended hammer strikingagainsta test vbar of the material to be examined.

One object of the present invention is to produce an apparatus, in whichthe hammer has a relatively small completely fiat impact surface whichremains practically constant regardless of wear and tear. I

Another object of the invention is to provide for an arrangement inwhich each individual test bar can be tested successively at a pluralityof different points in an easy and effective manner.

" A further object of the invention is to produce a device in which apointer suspended independently of the hammer is entrained by the latterin the direction of rebound only and is retained automatically in themaximum position, whereupon the hammer and the pointer may be reset totheir initial positions by means of a handoperated device.

The invention is illustratively exemplified in the accompanyingdrawings, in which Fig. 1 is a front elevational view, partly insection, of one embodiment of the invention.

Fig. 2 is a, substantially elevational side view of-the device shown inFig. l, with one of the outer parts omitted to show the innerarrangement and taken partly in section on line II-II of Fig. 1.

Fig. 3 shows a modification of the lower part of the apparatus in asectional view taken on a line corresponding to line III-III in Fig. 1.

Figs. 4 and 5 illustrate the upper portion of a modified form of theinvention in a partially sectional front view and in side elevation, re-

} spectively.

Referring now to Figs. 1 and 2, the apparatus comprises a base iprovided with two rollers 2 and 3 which support a cylindrical test bar 4of the material to be examined. The two rollers 2 and 3 allow an easyrotation of the test bar so that different parts of the same fiatsurface may be exposed successively to the rebound test.

During the test the bar is locked by means of a screw 5. The screw 5presses the test bar slightly against a lateral projection 6 of anupright I, which latter supports the pivot pin 8 of a hammer 9.

The hammer 9 is mounted on a ball bearing H] by means of an arm H whichis rigid and light at the same time. The mass of the hammer 9 consistspreferably of steel and has a suitable weight in proportion to thelength of the arm I l, to the striking surface and to the purpose thehammer is intended for.

The hammer 9 is formed as a lens-shaped mass 5 provided at its peripherywith a. small cylindrical pin I2 having a fiat base which forms thestriking face of the hammer.

The hammer 9, II is mounted free for a rotation of from the uppervertical position 10 down to the bottom-position. It is held in theupper position by means of a spring bufi'er and rocking leverv l3, I4. Astop pin i5 may be applied to a hole 5, in order to positively preventthe fall of the hammer 9. The upper rest posi- 15 tion of the hammer 9is determined exactly by a fixed stop ll when the apparatus has beenlevelled by means of adjusting screws Ill-l9 and 20. In this positionthere lies against the hammer a pawl 2| actuated by the feeble spring 222 bearing against plate 23. The spring actuated pawl 2! serves tolightly displace the hammer 9 by advancing the pawl 2! to the position2i when the point 24 of the rocking lever I4 is withdrawn from thehammer 9. The fixed stop ii 25 holds the pawl 2| in the position 2!.

A pointer 25 pivoting on the axle 8 indicates the degrees of rebound(that is the rebound angle) on the dial 116. For this purpose, thehammer 9, H is provided with a triangular projection 30 30 substantiallyin a plane perpendicular to the hammer rod II. The projection 30comprises an inclined cam surface to move the pointer 25 out of its pathwhen the hammer strikes down.- wardly, and is provided rearwardly with a35 straight surface, which engages thepointer, when the hammer rebounds,whereby the pointer is entrained by the hammer during the'upward strokeof the latter.

If desired the dial 26 may indicate, instead of 40 the degrees ofrebound the figures relating to the resistance to pressure per cm. ofthe'material to be examined, said figures being previously deduced fromcomparative experiments.

A stop 30" provided on the dial 26 locates the 5 pointer 25 in its zeroposition. The pointer 25 is provided with a device by which it isretained in the'position corresponding to the maximum rebound point. Inthe illustrated embodiment,

a small laminated spring 29 is inserted between 50 the ring 27 integralwith the pointer 25 and the fixed flange 28. The spring 29 causes aslight friction between the flange 28 and ring 2'! which does notprevent rotation of the pointer 25 but is suflicient to retain thepointer in the maxi- 55 mum position assumed after the first rebound ofthe hammer.

The present apparatus operates as follows.

A cylindrical test bar 4 of the material to be examined, is placed onits seat with the cylindrical surface resting on the rollers 2 and 3.The test bar is fixed by means of the set screw 5, care being taken thatthe perfectly flat base of the cylinder is presented to the impact ofthe hammer. Then the hammer is caused to swing down from its upperposition to a lowermost position in which the parts 9, I2 and assume thepositions 9, I2, and .3B'.(Fig. l), and to rebound from the test bar,whereupon the position 25 to which the pointer is carriedby therebounding hammer and in which it is automatically retained thereafter,can beread upon the dial. After releasing the test bar by slackening thescrew 5, the bar is rotated on the rollers Z and 3 and another zone ofthe same face is presented to the hammer impact. The operation isrepeated as often as necessary to obtain the desired approximation.

On the pin 8, there is mounted rotatably and axially displaceably a knob3! with an eccentric pin 32 fixed thereto. By shifting the knob 3| onthe pin 8, the pin 32 may be projected into the path of the hammer arm Il and may then be rotated in counter-clockwise direction to restore thehammer 9 to its uppermost position. During this movement, the pointer 25is carried along by the tooth 30 on the hammer 9, but is released fromsaid tooth when it strikes a tapered projection 38 provided on the upperportion of the dial 26 (see Fig. 2). Finally the knob 3| is released androtated in clockwise direction to restore the pointer 25 to its originalposition.

Fig. 3 illustrates a section taken substantially on line III-III of Fig.l but showing some modifications. The test bar 4 is supported, insteadof on rollers, on flat, tangential surfaces 2', 3, which are of asimpler construction. Furthermore a member 33 is fixed to the base I andprovided with a notch 34 whose bottom face 35 serves for tracing fourreference signs on the adjacent base of cylinder 4, while the upper face36 of said notch 34 may be referred to when the cylinder 4, between twosubsequent tests, is subjected to an angular displacement w to avoid therepetition of impacts on the same point.

Figs. 4 and 5 show another modification of the invention. The mass ofthe hammer 9" is of parallelepipedon-like form for simplifying theconstruction and is held in its upper position by means of a stop 24cooperating with a projection 31 of mass 9". The centre of gravity ofthe mass 9" is declined from the vertical by an angle 5, whereby thespring 22 of Fig. 1 can be omitted.

As shown clearly in Fig. 5, the mass 9 is held in position by atransversally projecting pin [5 having a knob handle at one end thereof.

The invention is not limited to the example of realization abovespecified and illustrated; changes may be introduced without modifyingthe characteristics as resulting from the following claims ortrespassing the gist of the invention. For instance the test bar may beof prismatic shape or of another form whatever, in this case the seatserving to fix the test bar will have consequently a form different fromthe cylindrical one.

Having now particularly described and ascer- "tained the nature of mysaid invention and in what manner the same is to be performed, 1 declarethat what I claim is:

1. In an apparatus for testing hardness, a frame comprising a supportfor a cylindrical test bar, and a hammer pivotally suspended on saidframe and being provided with a projecting impact pin to strike the baseof the cylindrical test bar at a point off center thereof, a lateralprojection upon said frame for accurately locating the fiat surface ofthe test bar in relation to thepoint of pivotal suspension of saidhammer, screw threaded means pressing and holding the test bar againstsaid projection, whereby physical displacement of said test bar uponimpact of the hammer therewith is prevented, and spaced supports for thetest bar whereby, upon the release of said screw threaded means,different portions of the fiat surface of the test bar may be broughtinto the operative relation to the plane of movement of the hammer.

2. In apparatus for testing hardness of materials a frame embodyingtherein a base having an upright extending therefrom, an arcuate gaugeextending from the top of said upright to adjacent said base, aprojection upon said upright, a screw threaded clamping member in axialalinement with said projection, spaced supports for a test bar parallelwith the axis of said clamp and said projection, whereby a test barhaving a fiat surface may be firmly mounted in relation to said basewith its flat surface accurately positioned in relation to said uprightand a may be angularly adjusted in relation to said projection, apendulous hammer mounted in said upright and having an impact pin havinga flat impact surface adapted to engage the flat surface of the testbar, a gauge finger co-operating CESARE ZAMBONI.

